1. Field of the Invention
This invention relates to footwear, and more particularly to an athletic shoe having an inflatable bladder.
2. Background Art
Athletic footwear must provide stable and comfortable support for the body while subject to various types of stress. It is important that the shoe be comfortable and provide support during various foot movements associated with athletic activity.
Articles of footwear typically include an upper and a sole, and are sold in a variety of sizes according to the length and width of the foot. However, even feet of similar length do not have the same geometry. Therefore, a conventional upper must be adjustable to provide support to various foot contours. Many different products and designs have focused on the need for adjustable upper support. For example, the upper may include an ankle portion which encompasses a portion of the ankle region of the foot and thereby provides support thereto.
In addition, it is well known to adjust the size of a shoe through lacing or through one or more straps reaching across the throat of a typical shoe. Lacing alone, however, suffers from several disadvantages, for example, when the shoe laces or strap is drawn too tightly, the fastening system can cause pressure on the instep of the foot. Such localized pressure is uncomfortable to the wearer and can make it difficult for the shoe to be worn for prolonged periods of time. Furthermore, while lacing allows the upper of the shoe to be adjustable to accommodate varying foot and ankle configurations, it does not mold the shoe to the contour of individual feet. Moreover, there are areas of the foot which are not supported by the upper, due to the irregular contour of the foot. The ski boot industry has often resorted to using inflatable insertable devices to improve the fit of the boots without the pressure caused by lacing.
One of the problems associated with shoes has always been striking a balance between support and cushioning. Throughout the course of an average day, the feet and legs of an individual are subjected to substantial impact forces. Running, jumping, walking and even standing exert forces upon the feet and legs of an individual which can lead to soreness, fatigue, and injury.
The human foot is a complex and remarkable piece of machinery, capable of withstanding and dissipating many impact forces. The natural padding of fat at the heel and forefoot, as well as the flexibility of the arch, help to cushion the foot. An athlete's stride is partly the result of energy which is stored in the flexible tissues of the foot. For example, during a typical walking or running stride, the achilleas tendon and the arch stretch and contract, storing energy in the tendons and ligaments. When the restrictive pressure on these elements is released, the stored energy is also released, thereby reducing the burden which must be assumed by the muscles.
Although the human foot possesses natural cushioning and rebounding characteristics, the foot alone is incapable of effectively overcoming many of the forces encountered during athletic activity. Unless an individual is wearing shoes which provide proper cushioning and support, the soreness and fatigue associated with athletic activity is more acute, and its onset accelerated. This results in discomfort for the wearer which diminishes the incentive for further athletic activity. Equally important, inadequately cushioned footwear can lead to injuries such as blisters, muscle, tendon and ligament damage, and bone stress fractures. Improper footwear can also lead to other ailments, including back pain.
In light of the above, numerous attempts have been made over the years to incorporate into a shoe a means for providing improved cushioning and resiliency to the shoe. For example, attempts have been made to enhance the natural elasticity and energy return of the foot with foams such as EVA, which tend to break down over time and lose their resiliency, or with fluid-filled inserts. Fluid filled devices attempt to enhance cushioning and energy return by containing pressurized fluid disposed adjacent the heel and forefoot areas of a shoe. Several overriding problems exist with these devices.
One of these problems is that often fluid filled devices are not adjustable for physiological variances between people and the variety of activities for which athletic shoes are warn. It has been known to adjust fluids in the sole of footwear, such as in U.S. Pat. No. 4,610,099 to Signori. However, under foot devices, while providing cushioning to the sole, typically do not aid in support for the sides, top and back of the foot. Attempts to cushion the upper and sole of a shoe with air have resulted in products that are either ineffective or, because of the construction techniques used, are too heavy and cumbersome to be used for a running shoe.
For example, U.S. Pat. Nos. 5,113,599 discloses an article of footwear having an inflatable bladder under the foot as well as around the sides and back of the foot. In conventional underfoot cushioning systems, when the heel contacts the ground during the gait cycle, fluid is transferred from the heel area of the foot and displaced to the forefoot area of the foot, causing the pressure in the forefoot area to increase. Because the underfoot portion of an inflatable bladder is typically separate from the portions of an inflatable bladder along the sides and top of the foot, downward pressure in the heel of a conventional cushioning device has no effect on the cushioning surrounding the sides and heel of a foot.
Conventional inflatable shoe inserts are also designed to be used in conjunction with a conventional shoe upper. A shoe with this type of design can be quite expensive because it requires all the materials of the upper and the additional materials of the inflatable insert. Often the inflatable inserts also add bulk to the shoe because they require a system of complex tubing between the inflation mechanism and the inflatable bladder. With the presence of an upper to completely surround the foot, there is no need for the inflation inserts to completely surround the foot. Conventional inserts may only support certain regions of the foot.
Most conventional inflatable shoes include either a hand-held inflation mechanism, e.g., that described in Brazilian Patent No. 8305004 to Signori, or an on-board inflation mechanism which is used to selectively inflate only a portion of a shoe. Other inflatable shoes are pre-inflated at the factory. Whether inflated at the factory or inflated by the user, there is a problem with diffusion of air out of the shoe. In the case of shoes inflated at the factory, the problem of diffusion has been partially solved by utilizing a large molecule gas as the fluid for inflating the shoe. While the large molecule gas does not diffuse at the same rate as air, the gas is more expensive which increases the costs of the shoe, and a user is not capable of varying the amount of pressure in the shoe to his individual preferences.
Accordingly, what is needed is a shoe which includes one continuously fluidly interconnected inflatable bladder, wherein fluid may flow between the underside of the foot to the medial and lateral sides of the foot without the need for complex tubing. The footwear must be securely fitted and fastened to the foot of the wearer, whereby a comfortable but secure grip is assured around the ankle and around the instep of the wearer. Further, the bladder in the athletic shoe must be lightweight, inexpensive, self-contained, and easy to use. In addition, the shoe should be easily constructed with minimum required stitching.